The invention relates to scanning-based ionizing radiation detector arrangements for two-dimensional detection of an object.
Gaseous-based ionizing radiation detectors, in general, are very attractive since they are cheap to manufacture, can employ gas multiplication to strongly amplify the signal amplitudes, and provide for detection with high spatial resolution.
A particular kind of gaseous-based ionizing radiation detector is the one, in which electrons released by interactions between photons and gas atoms can be extracted in a direction essentially perpendicular to the incident radiation. Hereby, a strongly improved spatial resolution is achievable.
Such a detector comprises typically planar cathode and anode arrangements, respectively, and an ionizable gas arranged in the space formed between the cathode and anode arrangements. The detector is arranged such that a planar radiation beam from a radiation source can enter the detector sideways between, and essentially parallel with, the cathode and anode arrangements for ionizing the ionizable gas. Further, a voltage is applied between the electrodes for drifting, and optionally multiplying, electrons created during ionization of the ionizable gas. A readout arrangement is arranged in connection to the anode for detecting the charge induced by the drifted electrons.
The detector obviously provides for instantaneous one-dimensional imaging, but to perform two-dimensional imaging the detector, and optionally the radiation source, have to be moved in a direction traverse to the one-dimensional detector array relative to an object being examined while several readouts are recorded. Such scanning-based two-dimensional detection is however time consuming and is impractical if large areas should be imaged. Further, if the object being examined is a human or an animal there is a risk that the human or animal moves during scanning, which could make the image useless or at least severely reduce the spatial resolution obtained.
To reduce scanning time a stacked detector arrangement has been proposed in U.S. Pat. No. 6,118,125 by Francke at al., with which multi-line scans can be achieved. The arrangement includes an X-ray source, which together with a number of collimator windows produce a stack of planar fan-shaped X-ray beams for irradiation of the object to be imaged. The beams transmitted through the object enter the stacked detectors, optionally through a number of second collimator windows, which are aligned with the X-ray beams. The arrangement is moved as a unit to scan an object, which is to be examined.
In some radiological applications, however, there is a need to provide an image of an object to be examined at high speed in order to observe time-dependent variations. Such applications include, inter alia, recording of series of images to observe time dependent examination, such as e.g. positioning of catheters, and to visualize matter in motion, such as e.g. heart, blood, etc.
The present inventors have noticed that a stacked detector arrangement as the one described in U.S. Pat. No. 6,118,125 is impractical for imaging at high repetition rates. The imaging is performed by a transverse scanning movement, perpendicular to the X-ray beam, and thus the direction of scanning has to be altered for each further image to be recorded. Accordingly, the detector arrangement has to be decelerated, stopped, and accelerated in a reverse direction for each further image recorded and such actions are time-consuming and suffer from stability and alignment problems due to the strong forces the detectors experience during the decelerations and accelerations.
A main object of the invention is therefore to provide a scanning-based ionizing radiation detector arrangement for two-dimensional imaging of an object, which is capable of imaging at high repetition rates without encountering problems of stability or alignment.
A further object of the invention is to provide such a detector arrangement, which comprises a plurality of line detector units in a dense matrix to shorten scanning time and distance for each image recorded.
A yet further object of the invention is to provide such a detector arrangement, which is reliable, accurate, inexpensive, and which has a long lifetime.
These objects, among others, are attained by detector arrangements as claimed in the appended claims.
The inventors have found that by arranging ionizing radiation detector units, well suited to be volume produced with high precision, in an array, and by providing a rotating device for rotating the detector array in one rotation direction only in the plane of the detector array, while detecting repeatedly, a scanning-based detector arrangement for highly resolved two-dimensional imaging of objects at high repetition rates is provided.
Further characteristics of the invention, and advantages thereof, will be evident from the detailed description of preferred embodiments of the present invention given hereinafter and the accompanying FIGS. 1-8, which are given by way of illustration only, and thus are not limitative of the present invention.